Modern automated manufacturing machines commonly perform hundreds of operations a minute requiring rapid, accurate and repeatable movements. Manufacturing machines typically have a material removal tool, such as a drill bit, which performs multiple operations on a workpiece. The drill bit rotates in a spindle while the workpiece is held on a worktable in a known orientation. The pattern to be machined is predetermined and stored in the memory of a support computer which then controls the relative movements of the spindle and workpiece. In some drilling applications, such as the drilling of holes in printed circuit boards (PCBs), the scale of the operation is reduced to extremely small dimensions.
PCBs are used in practically all types of electronic equipment, radio and television sets, guided missiles, computers, etc. PCB is the designation given to a complete circuit printed onto one or both sides of an insulating board, resulting in a complex yet space-efficient, modular electronic component. In the production of PCBs, numerous holes must be drilled in the insulating board to accommodate the leads of the discrete components secured to the board. Holes are also lined or plated with copper to connect the circuits etched into the copper film of PCB layers in a stack. Furthermore, holes are required to permit the secure mounting of the PCB itself to the inner structure of the host device. As a result, in many cases, literally thousands of holes must be drilled into each of the PCB insulating boards to enable the above-referenced assemblies to be made. The precision machining of these holes is critical in the manufacturing of PCBs.
Another application requiring extreme precision is the use of stacks or layers of PCBs, bonded together to create larger circuits. By necessity, the circuit pattern is etched onto the inner layers prior to any drilling, and thus the holes through the layers must exactly match up with the existing circuit, or the board is useless. Many of the numerous components on complex PCB's are extremely small in size, in order to maximize the efficient use of space, thus providing a dense environment of components. Hole size can be as small as 0.004 inches in the most complex boards. Such hole size requires utmost precision in the placement and drilling of the holes in the PCBs' due to the lower tolerance values associated with the micro-circuitry layout. Normally, the majority of PCB's cost less than $100 as a finished product, but some applications, such as a "mother" board for a supercomputer, might cost up to $15,000. Where PCBs are stacked, it will be appreciated that greater processing charges have been incurred prior to the drilling process. Thus, it becomes even more important to precisely control the drilling operation to avoid drilling errors which would render the board worthless.
For years, efforts have been made to improve the precision of PCB drilling machines. These efforts have generally focused on precisely controlling the movement of the spindle and work table relative to one another. However, particularly with the drilling of stacked PCBs, further breakthroughs are necessary to avoid errors and wasted materials and effort.